Method of heating fluids



Dec. 17,1940. L. A.

METHOD OF MEKLER 2,224,917

.HEAT ING FLUIDS Original Fi led Dec. 26; 1931 I 0 7 lo O v 0000 n 1 1l5 l7 4/ 0000d000 FIG. I

TEMPERATURE OF FLUID PERCENTAGE OF HEATING SURFACE FIG. 3

INVENTOR LEV A. MEKLER ATTORNE Patented Dec. 17, 1940 PATENT OFFICEMETHOD OF HEATING FLUIDS Lev A. Mekler, Chicago, 111., assignor, bymesne assignments, to Universal vOil Products Com pany, Chicago, 111., acorporation of Delaware Application December 26, 1931," Serial No.583,341

' Renewed November 10, 1938 1 Claim.

many of these furnaces may be easily converted into more eflicientheating units, employing the more modern methods of combination radiantand convection heating, by adding, inaddition to the existing bank ofconvection tubes, a row of radiant tubes in the upper portion of thefurnace along the roof and along a portion ,of the Walls and by adding arow .of radiant floor tubes along the floor of the combustion zone ofthe furnace. Preferably the old firing arrangement is changed and theimproved furnace is fired throughoneor a-plurality of firing tunnelsextending into a side of the furnace and having air inlet ductssubstantially surrounding or adjacent the firing compartment thereof.

In its specific embodiment the present invention comprises an improvedform of furnace for heating fluids having a combustion zone, means forsupplying combustible materials to said combustion zone, a convectionheating zone, a bridge wall separating said combustion zone from saidconvection heating zone, fluid conduits disposed along the floor of saidcombustion zone receiving substantially radiant heat, fluid conduitsdisposed along'the roof and upper portion of the walls of the furnace toreceive substantially radiant heat and fluid conduits disposed withinsaid convection heating zone to receive substantially convection heat.

The arrangement of the heating element, i.- e., the conduit throughwhich the fluid is passed during heating, as provided by the apparatusof the invention, is especially well adapted to a flow of fluid whichresults in an improved heating method and which is especiallyadvantageous in heating hydrocarbon oil to the relatively hightemperatures utilized in their conversion or cracking. Ihis methodcomprises subjecting the oil, during the initial stages of its heating,toa relatively high rate of heating to bring it quickly to a conversiontemperature, thence subjecting it to continued heating at a somewhatslower rate and finally again subjecting the oil to a relatively rapidrate of heating to bring it to the maximum temperature employedsubstantially at the outlet from the heating element. This may beaccomplished in the apparatus of the present inventionby passing the oilfirst through the floor bank of I radiant tubes, thence through theconvection bank of tubes preferabIy countercurrent 5 to' the flow ofcombustion gases and finally through the radiant bank of tubes disposedalong thereof and sides of the furnace.

The attached diagrammatic drawing illustrates one formof apparatus forcarrying out the 10 method of the present invention. Figure l is across-sectional elevation of the furnace. Figure 2- illustratesdiagrammatically the preferred flow of fluid through the heating elementof the furnace illustrated in Figure 1,. Figure 3 illustrates thegeneralform of heating curve obtainable by employment of the improvedheating means illustrated in Figures 1 and 2.

Referring nowipar'ticularly to Figure 1, the side walls are indicated atI and 2, the roof is indi- 20- cated at 3 and the floor of thecombustion zone 4 is indicated at5. "A'bridge wall6 separatescombustionzone 4 from convection heating zone 1.

One or a plurality of firing tunnels 8, disposed along side wall I ofthe furnace, furnish means of supplying combustible materials tocombustionzone 4'; Any suitable fuel such as, for ex-v ample, 'o'il,pulverized solid fuel, gas or the like, may be introduced through anysuitable burner arrangement, not shown, to firing compartment 30 9, oftunnel 8. 'Ducts l0 and H, adjacent firing compartment 9, serve as ameans of introducing air, steam or both to the combustion zone of thefurnace, the admission of such materials being regulated by dampers l2.

The combustion gases pass upward through combustion zone l overbride-wall 6, downward throughjconvectionheating zone I and out of thefurnace to'a stack, not shown,through flue l3. i

A row or bank ll of tubes I5, preferably connected at their ends inseries by suitable return bends, headers or other well known means notillustrated, is disposed along the floor 5 of combustion zone 4.Preferably radiant bank I4 is depressed below the level of firingcompartment 9 sufliciently to prevent any substantial direct impingementof flame upon the tubes. A radiant bank or row l6 of tubes I5 isdisposed along the upper portion of the furnace, adjacent roof 3 andwalls I and 2. That portion of bank I6 adjacent wall I of the furnacemay, if desired, be recessed, as illustrated in the drawing, tosubstantially prevent flame impingement against the tubes. A convectionbank I! of tubes I5 is disposed within 55,

" conversion temperature and, second, by virtue of ture, by having firstpassed through another porconvection heating zone 1 of the furnace,being separated from combustion zone 4 by bridge wall 6. The tubes ofradiant bank I6 and convection bank I! are also preferably connected inseries, as already mentioned in connection with radiant bank I4. Radiantheating banks I4 and 16 receives substantially radiant heat from the hotcombustion gases and-from the heated refractory walls of the furnacewhile convection bank I'I receives substantially convection heat fromthe somewhat cooler combustion gases passing downward through convectionzone 1 around the tubes of said convection bank.

It will be apparent from the drawing, that'the tubes of the radiantfloor bank [4 aresubjected to more severe conditions than thetubes oftheother heating banks in the furnace and unless fluid to be heated,first into the radiant floor bank l4, serves a two-fold purpose. Firstit provides a means of rapidly bringing the oil to a the relatively coolcondition of the oil entering this bank of tubes, said tubes areprotected against such overheating as might result if the oil wereintroduced thereto at a higher temperation of the heating element.

Referring now to Figure 2 which diagrammatically illustrates thepreferred flow of fluid through the heating elements of a furnace suchas illustrated in Figure 1. The radiant bank of floor tubes is againindicated at l4, the convection bank is indicated at IT and the radiantroof and wall bank at It. Theoil to be treated is 40? introduced throughline [8 into the first tube of radiant floor bank I4, passing throughthe sucsucceeding tubes of this bank in series, transdicated inFigure 1) of the furnace, j passing "the upper portion of wall I(indicated in Figure ferring thence through line 20, which is alsopreferably located outside the heating zone, to the lower tube of thatportion of radiant bank IS, located along the upper portion of wall 2(inthence through the succeeding tubes of radiant bank 16 in series andout of the furnace through line 2|, being dischargedfrom the lower tubeof that portion of radiant bank I6, located along 1) of the furnace.

Figure 3, as already stated, indicates the gene eral type of heatingcurve which may be obtained by utilizing the form of furnace illustratedin,

Figure 1 and a flow of fluid through the fluid conduit of this furnace,as illustrated in Figure 2. It will be noted from the heating curve andby comparison of this curve with the flow diagram of Figure 2 that theoil is first heated in the radiant floor bank M at a relatively highrate, that the temperature obtained in this zone is gradually increasedat a slower rate of heating in convection bank l1 and is thence againsubjected to a relatively rapid rate of heating in radiant bank l6,discharging from this zone at the maximum temperature attained in thefurnace. Those conversant with the cracking art will, appreciate theadvantages of this type of heating curve in the conversion of many typesof oils. Its primary advantages reside in the fact that the oil may befirst rapidly raised to a relatively mild conversion temperature, may bethence maintained at a gradually increasing but relatively mildconversion temperature for an eX- tended period of time and may bethence rapidly brought to the maximum conversion temperature desired.This procedure not only minimizes local overheating of the oil withconsequent excessive gas and coke formation but also serves as a meansof protecting that portion of the fluid conduit which is subjected tothe most severe heating conditions by feeding the oil therethrough whilesaid oil is still relatively cool.

It will be understood that the invention is not limited to theparticular flow of fluid illustrated in Figure 2, nor to the specificform of furnace illustrated in Figure 1, nor to the type of heatingcurve indicated in Figure 3, as the principles involved may beaccomplished in modified forms of apparatus and under different heatingconditions whichv do not depart from the scope of the invention. v

I claim as my invention:

In the heating of hydrocarbon oils to cracking temperature in furnaceshaving a pair of side walls, a floor and a roof and, av bridge walldividing the furnace into a, convection heating zone and aradiantheating zone, the method which comprises firing the furnace adjacent thelower portion of the radiant zone and passing resultant combustion gasesthrough the convection zone, passing the ,oil initially through tubesadjacent the floor to raise it quickly to mild cracking temperature. ata relatively high rate of heating, thence passing, the oil through theconvection zone tosubject itto continued heating at a lower rate ofheating, and .then raising theoil to maximum cracking temperature undera relatively high rate of heating by passing it through tubes adjacentthe side wall nearer the convection zone, then through tubes adjacentthe roof and finally through wall tubes on the firingside of-thefurnace.

LEV A. MEKLER.

